Understanding the role of process parameters in 4D printing: A review

4D printing was initially defined as multi-material 3D printing that can produce pre-programmed shape changes under external stimuli over time. Thus extensive research relies on multi-material-based design to manipulate the deformation of 4D printed objects. An easy to neglect fact is that printing parameters are also dominant factors affecting the microstructure and properties of the printed objects. Parameter-encoded programming strategy endows 3D printing with exclusive capabilities in building site-specific gradient/ordered structures, and thus confers preprogrammed anisotropic/nonlinear shape morphing responses to printed structures. In this work, we provide a comprehensive review of recent advances in parameter-encoded 4D printing and highlight how the structure-property of the printed materials was refashioned by exerting control over the process parameters. The review expects to shed light on understanding the role of parameters in 4D printing and opens up a new design space through parameter-encoded design, which helps truly unleash the potential of this emerging and promising technology.